The invention generally relates to a power recycling technique used to enhance the efficiency of radio-frequency (RF) amplifiers based on the Envelope Elimination and Restoration (EER) technique.
Linear modulations such as MPSK and MQAM are desired for mobile wireless communications because of their superior spectral efficiency, but they require linear power amplification at transmission. On the other hand, limited battery capacity imposes primary restrictions on the power consumption of the typical mobile handset, and even base station power amplifiers have limited DC power availability. In a typical transceiver architecture, it is typically the final power amplifier stage that constitutes these real challenges for the designer. Many linearization techniques have been proposed to improve the linearity of the power amplifiers while at the same time enhancing the power efficiency. Often there may be energy lost in filtering of high frequency harmonics, and thus it is desirable to minimize these losses for power efficiency.
In Conventional Envelope Elimination and Restoration (EER) RF amplifier design (as depicted in FIG. 1), the modulated signal is separated into carrier 110 and envelope 120 components. Each of these components is amplified in a power-efficient manner by EER 130 and then recombined to create the amplified RF output 140. Processing of the carrier component is performed by a saturated amplifier 150; as a result, output 160 prior to filtering contains the modulation imposed on a square-wave carrier.
Diplexer 170 following saturated amplifier 150 has two functions: (1) lowpass filter—the amplified content to provide harmonic and broadband noise reduced spectral content for transmission by a lowpass filter 180, and (2) high pass filter—the amplified content, by a highpass filter 190, to direct the harmonic and broadband noise to a termination at load 195. In addition, diplexer 170 assures that saturated amplifier 130 sees a constant load impedance independent of frequency.
From Fourier series theory, the power in the fundamental component of a square wave comprises 81% of its total power, and the harmonic components comprise the remaining 19% of its total power. As an example, assuming the diplexer filters are lossless, 25 watts of square-wave energy would yield about 20 watts of desired fundamental component RF output energy and about 5 watts of undesired harmonic energy dissipated in the load.
If the harmonic energy dissipated in the load can be recovered and used to help power the RF amplifier, then the amount of DC power required would be reduced and the overall power efficiency of the amplifier would increase. Reduced power consumption also reduces the amount of thermal dissipation required, which in turn reduces the amplifier's size and weight.
Accordingly, there is a need for a power recycling technique to enhance the efficiency of radio-frequency (RF) amplifiers based on the Envelope Elimination and Restoration (EER) technique. There is a need for a technique which uses a “harmonic energy recovery” circuit, in which a portion of the power wasted in harmonic content generation can be recovered, allowing the amplifier to draw less DC power and thus be more power-efficient, as well as potentially smaller in size and weight due to a requiring a lower thermal mass.
The techniques herein below extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned needs.